A shock sensor or impact monitor is a device that detects if certain physical shock or impact has occurred. Shock sensors are often used in the shipment of fragile, valuable items to indicate whether a potentially damaging drop or impact of the item may have occurred during transport.
Examples of shock sensors include accelerometers using microelectromechanical (MEMS) systems, spring-mass systems, magnetic balls which can be dislodged from a holder, liquid systems that monitor disruption of the liquid surface tension, devices made of inexpensive brittle components with a known fragility where breakage indicates excessive shock, etc. For instance, a common commercial shock sensor used during shipping simply includes a label having a liquid indicator that visibly changes color when rough handling (above a certain threshold value such as 25 g) occurs—where g is the acceleration of gravity.
One drawback to conventional shock sensors is that many of the above examples are limited to detecting a preset threshold, such as 25 g, of shock. Different items are, however, sensitive to different levels of shock. Since the sensitivity of conventional shock sensors is not tunable, a different sensor must be used to change the sensitivity. Another drawback is that most conventional shock sensors are one-time use only. Once the sensor is tripped, the change is permanent and the sensor must be replaced.
Therefore, improved shock sensor designs that are tunable, high sensitivity and resettable would be desirable.